Stress on stress response of wild mussels, Mytilus edulis and Mytilus trossulus, as an indicator of ecosystem health.

Mussels' health as indicated by the survival time of 50% of sampled animals (LT(50)) when maintained in air at 15 degrees C was examined at three sites in Halifax Harbour with expected differing levels of contamination. Condition and gonad indices, lipid content and the body burden of polycyclic aromatic compounds (PACs) were compared with this stress response in 60 groups of mussels covering two species. At each sampling time, the bioaccumulation of PACs, lipid content and condition indices were higher within Mytilus edulis and Mytilus trossulus displaying shorter survival than at the other sites. M. edulis was generally more tolerant than M. trossulus (for n=11, LT(50) of 9.3 and 7.9 days), with indications of shorter and later gonad development in M. trossulus. Minimum and maximum tolerance was apparent in June and October (LT(50) spanning 3-14 days), respectively. Our results indicate that the stress on stress response provides a simple and sensitive indicator of environmental health, which could be integrated with mussel watch studies.